Method and apparatus for bending tubing



Oct. 21, 1969 J. A. CWIK 3,473,361

METHOD AND APPARATUS FOR BENDING TUBING Filed April 6, 1967 5 Sheets-Sheet 1 INVENTOR JOSEPH A. CWIK ATTORNEYS Oct. 21, 1969 J. A. CWI K 3.473.361

METHOD AND APPARATUS FOR BENDING TUBING Filed April 6. 196'? 5 Sheets-Shae? 2 'INVENTOR JOSEPH cwm ATTORNEYS Oct. 21, 1969 v I J cwm 3,473,361

, I METHOD AND APPARATUS FOR BENDING TUBING Filed April 6. 1967 5 Sheets-Sheet :s

4 INVENTOR JOSEPH A cwm ATTORNEYS Oct. 21,1969 J. A. CWIK I um'aob up APPARATUS FOR assume TUBING 5 Sheets-Shae? 4 Filed April 6. 196'! INVENATOR JOSEPH A. CW/K ATTORNEYS Oct. 21, 1969 J. A.CWIK I 3,473,361

I HETHODAND APPARATUS FOR BENDING TUBING I I Filed April 6, 1967 I 5 Sheets-Sheet s INVENTOR JOSEPH A. CWIK ATTORNEYS United States Patent 3,473,361 METHOD AND APPARATUS FOR BENDING TUBING Joseph A. Cwik, Denver, Colo., assignor, by mesne assignments, to Teledyne, Inc., Los Angeles, Calif., a corporation of Delaware Filed Apr. 6, 1967, Ser. No. 628,919 Int. Cl. B21d 9/05, 21/00; H02k 7/00 US. Cl. 72150 22 Claims ABSTRACT OF THE DISCLOSURE Tube bending machine of conventional construction plus a high frequency mechanical force generator coupled to tooling or workpiece to impart high frequency vibratory forces to the workpiece at the bending zone. Generator is activated during bending operation to render workpiece material semi-plastic in character to reduce resistance to bending and cause metal flow from inside of bend to outside of bend and reduce wall thickening and thin-out to minimum. Surface wave effect reduces friction between workpiece and tooling.

Background of the invention This invention lies in the field of tube bending and relates to methods and apparatus for producing bends of any desired extent and curvature in metallic tubing in a superior manner. It is particularly directed to a method of treating metallic tubing at the time and location of bending to reduce friction force and resistance to deformation, and to apparatus with which the method may be practiced.

The conventional tube bending apparatus which is in wide use at the present day comprises only a few essential components to accomplish the actual bending operation, and various accessories are used to reduce the manual work required, to improve the quality of the bend, and to render the machine more or less automatic. A bend die is normally mounted on a support for rotation about a vertical axis and is provided with an arcuate peripheral portion having a semi-circular groove to receive one side of the tube to be bent. It also has a tangential extension of the grooved periphery to receive a straight portion of the tube, and an opposing grooved clamp die which is forced toward the extension to grip the tube therebetween for drawing. The die is rotated manually by a handle or mechanically by power applied to the mounting shaft to draw succeeding portions of the tube into the peripheral groove and produce the desired bend.

The advancing tube section is confined to straight line motion by suitable means such as a pressure die mounted in opposition to the bend die. When the nature of the tube or bend is such that the tube is likely to collapse in bending, a mandrel is provided which has a free end extending into the tube, usually with a flexible extension which may follow the outline of the bend. The mandrel has a reduced diameter rear extension which extends rearwardly beyond the end of the tube and is secured to an anchorage to maintain it in place during the bending operation.

Tubes which are fairly large and thick-walled may be readily bent around curves which have a centerline radius (from the centerline of the tube to the axes of the bend die) of 'two or more times the diameter of the tube, and this has been satisfactory for the majority of the bending work which was required in the past. However, in recent years there has been a great increase in the proportion of diflicult bend requirements. These include bends with radii of one diameter or less, the use of tubing with very thin walls in proportion to their diameter, and the use of so-called exotic materials for tubing.

3,473,361 Patented Oct. 21, 1969 It will be apparent that as the bend radius ratio decreases, the percentage of stretch or attenuation at the outside of the bend and compression at the inside of the bend increases. Thus, the inner wall portion thickens to an undesirable extent and may ripple or buckle while the outer wall portion becomes so thin that it fails during forming or will fail in use at fluid pressures for which it was intended. The failure tendency is greatly increased with very thin-walled tubing, and it is almost impossible to prevent buckling of the inner wall. The exotic metals are brittle and have a very low elongation factor and cannot be bent beyond a few degrees with any previously known technique.

Various other problems have always been present even with conventional metals such as steel, copper, brass, and aluminum and with easier bends. Since the materials are somewhat elastic they tend to spring back when released and enlarge the bend so they must be overbent to compensate, and this involves guesswork. They are also subject to galling, spalling, and orange-peeling. Considerable power is required to overcome bend resistance and the friction of the tube on the mandrel and the pressure die.

Summary of the invention The present invention substantially overcomes or alleviates the problems mentioned above and has various other advantages which result in a greatly improved final product. Generally stated, the bending machine or apparatus which is used may be substantially the conventional type, including bend die, clamp die, pressure die, wiper die, mandrel, and means to rotate the bend die. The actual bending takes place in a very short distance of travel of the tube commencing at the point where the tube begins to depart from its original straight line form. The incremental bends follow around the arc as the bend die rotates with little or no further change or shape. The area surrounding this point of departure, where the bend die and the pressure die most closely approach each other, is termed the bending zone and is generally defined by the tooling components.

The improvement in the bending operation is accomplished by changing the character of the tubing material in the bending zone. This is done by applying to this localized area of the tube a high frequency vibratory mechanical force of sufliciently high intensity to cause virtual slip-plane response in the sense of repeated unpinning of particles or molecules of the crystal lattice during one part of the stress cycle and elastic collapse and repinning during the other part of the cycle. The functional effect is to render the material semi-plastic in character so that it will flow readily in the same general manner as during a hot forging operation. The sharp drop in apparent static shear strength greatly reduces the force necessary for bending.

The bend die exerts a high radially outwardly directed force against the tube, and this force combines with the compressive force on the inside of the bend to cause peripheral flow of metal radially outward to the attenuated wall at the outside of the bend. During the incidence of ultrasonic agitation it has been observed that the elongation properties of the material to be bent have not only been greatly increased but have also allowed flow to occur over a much larger span. For example, the peripheral stretch zone has been found to extend much beyond the point of tangency and into the clamp and pressure die areas. The net result is less thickening of the inner wall and less thin-out of the outer wall.

In addition, the propagation of waves on the surface causes cyclical separation of the surfaces of the tube and tooling and greatly reduces the friction between them,

thus further reducing the power necessary to form the bend while at the same time reducing the amount of strain being transmitted into the tubing.

The vibratory energy is provided by a standard transducer of the piezo-electric or magnetostrictive type. The transducer with its horn or reed constitutes a high frequency mechanical force generator which may directly contact the tube, but preferably it is coupled to one of the tooling components. The tooling in turn transmits and applies the vibratory energy to the tube at the bending zone. The force generator may be activated only while the bending operation is in progress but preferably it is activated immediately prior to the bending operation.

Brief description of the drawings Various other advantages and features of novelty will become apparent as the description proceeds in conjunction with the accompanying drawings, in which:

FIGURE 1 is a schematic view in perspective of a typical tube bending machine incorporating a high frequency mechanical force generator coupled to a portion of the tooling to carry out the invention;

FIGURE 2 is a sectional plan view of the die portion of the machine of FIGURE 1;

FIGURE 3 is a schematic plan View of a modification of the apparatus of FIGURE 1;

FIGURE 4 is a schematic plan view showing a further modification;

FIGURE 5 is a schematic plan view showing a further modification;

FIGURE 6 is a schematic plan view showing a further modification;

FIGURE 7 is a schematic perspective view showing a bend die having a movable portion coupled to the force generator;

FIGURE 8 is a similar view showing the bend die directly coupled to the force generator;

FIGURE 9 is a similar view showing a modified type of force generator;

FIGURE 10 is a similar view showing a further modified type of force generator;

FIGURE 11 is a sectional view of a tube formed in a conventional bending machine;

FIGURE 12 is a sectional view of a tube formed in a bending machine incorporating the invention;

FIGURE 13 is a plan view of a modified type of bending machine;

FIGURE 14 is an elevational view of the bending machine of FIGURE 13;

FIGURE 15 is an elevational View of a multiple crystal, piezo-electric transducer;

FIGURE 16 is a right end elevational view of the transducer shown in FIGURE 15;

FIGURE 17 is a plan view of a portion of a tube bending apparatus using a rotatably mounted, circularly shaped, piezo-electric transducer in lieu of a conventional pressure die; and

FIGURE 18 is a cross-sectional view of a tube which has been bent in accordance with the method and apparatus of the instant invention.

Description of the preferred embodiments Suitable apparatus for practicing the invention is illustrated in FIGURE 1, in which a support in the form of a table 10 carries a set of tooling 14 and a high frequency mechanical force generator 16. The tooling includes .a bend die 18 and its tangential extension 20 fixedly mounted on plate 22 for rotation about the axis of vertical shaft 24 which is mounted on table 10. Clamp die 26 is mounted on plate 22 for movement toward and away from extension 20 by means of pins 28 and elongate slots 30. The plate and the aforesaid tooling elements are rotated manually by lever or handle 32 which is pivoted to the plate by pin 34. Lateral boss 36 on lever 32 engages the clamp die when the lever is moved in the direction of the arrow and forces the clamp die toward the bend die to grip tube 38 for the bending operation.

As the bend die rotates, it tends to swing the tube laterally, and this movement is resisted by pressure die 40 which guides the tube in its longitudinal movement and serves as a back stop to support the tube against reverse lateral movement. A wiper die 42 may be provided to serve its usual purpose of preventing rippling or buckling of the inner wall of the tube as it enters the bending phase. These four dies are provided with semi-circular grooves to receive the tube in the usual manner. It will be appreciated that the grooves which receive the tube may be formed in any one of several configurations such as rectangular, square or circular. Pressure die 40 is backed up by carriage bearings 44 and may be provided with a boost cylinder 46 if desired.

As best seen in FIGURE 2, a mandrel 48 is located within the tube with its forward end 50 substantially at the tangent point 52 where the bending action begins. The mandrel is provided with a multi-ball flexible extension 54 which is adapted to assume the curvature of the tube as the bending progresses and prevent the tube from flattening or collapsing. The mandrel is also provided with a rearwardly directed extension rod 56 which may pass through bearing 58 and is attached to a piston, not shown, in retract cylinder 60, FIGURE 1. The cylinder retains the mandrel in the position of FIGURE 2 during the bending operation and is actuated to pull the mandrel rearwardly at the conclusion of the operation to free it from the tube. All of these operations are conventional in present day bending practice.

The area 62 generally surrounding point 52 where bending commences is referred to as the bending zone, and some portions of the bend die and the pressure die, as well as the free end 50 of the mandrel may be stated to be at the bending zone. The character or condition of the metal as it is being bent is rendered semi-plastic by applying high frequency vibratory mechanical energy to the portion at the bending zone. The force generator for this energy is shown at 16 in FIGURE 1 and may be a standard piezo-electric or magnetostrictive transducer 64 having a horn or reed 66, the free end of which is coupled to a collar 68 on mandrel rod 56. Vibrations are imparted to the rod perpendicular to its axis and are transmitted to the free end 50 of the mandrel which vibrates laterally within the tube at the bending zone. The vibration applied or transferred to this portion of the tube from the mandrel renders it semi-plastic so that the force necessary to bend it is greatly reduced.

In conventional bending, the compression forces in the inner wall of the tube at point 70 cause it to thicken and the stretching or attenuation forces in the outer wall at point 72 cause it to thin out, often to the point of actual or incipient failure. This is illustrated in FIGURE 11, where it will be seen that the outer wall 76 is greatly reduced in thickness while the inner wall 78 is thickened excessively. Since the compressive yield strength is usually greater than the tensile value, the neutral axis NA. is to the right of the geometric axis G.A., or toward the inside of the curve or bend. When the tubing is orginally very thin-walled, the compression forces tend to buckle the inner wall as the bending takes place.

However, in the practice of the present invention, the outward radial pressure of the bend die, as represented by arrows 74, combined with the compression at point 70, causes actual peripheral flow of metal toward point 72. While the thicknesses do not remain completely uniform, the thin-out at point 72 is reduced well below anything achievable in conventional bending, and the thickening at point 70 is likewise reduced so that rippling or buckling is practically eliminated. This is illustrated in FIGURE 12, where it will be seen that the reduction in the compressive yield strength of the semi-plastic material makes it possible in some cases to shift the neutral axis N.A. to a location outside the geometric axis G.A.

Thus, through the use of the apparatus and method of the herein invention, excellent bends may be obtained which heretofore have been impossible.

The absorptionof energy during vibration results in a certain amount of heating of the metal which further aids in the softening and keeps work hardening stresses from forming during the bending operation. The repeated unpinning and repinning of the particles substantially eliminates residual stresses in the formed tube and consequently substantially eliminates spring back. For the same reason, the orange peel effect is eliminated,

-The surface wave effect achieves repeated momentary separation of the surfaces of the tube and tooling, and friction is so greatly reduced that in many cases no lubrication is required. An additional and very important benefit derived from this feature is that the surfaces of the processed tubing are far smoother than heretofore.

The energy intensity required for a given operation cannot be specified with any exactitude because it depends on the size of the tube and the material of which it is made. Also, the amplitude of vibration is variable inversely to the frequency. Although, beneficial results have been obtained with amplitudes varying between 0.0001 to 0.005 inch, good results have been obtained with amplitudes of 0.002 to 0.005 inch. The input frequency is preferably in the ultrasonic range, from 18,000 to 100,000 cycles per second, but good results have been obtained in the upper portion of the sonic range.

Since the waves propagated in the tube travel in various directions at angles to the direction of the applied vibration, it is feasible to apply the vibration in axial as well as lateral directions. In FIGURE 3, for instance, most of the components are arranged in the same way as in FIGURE 1, but mandrel rod 56 is coupled to the horn 66 of the force generator 16 and the retract cylinder 60. Consequently, the vibrations travel longitudinally of the mandrel rod and are delivered in a longitudinal direction at free end 50 in the bending zone 62. Since the waves propagate in various directions, the results are comparable to those of FIGURE 1. However, it has been found that the standing waves generated are not as pronounced when the force generator is mounted as shown in FIG- URE 3 as compared to the mounting shown in FIGURE 1. Thus, the effect of the standing waves is less critical with the mounting shown in FIGURE 3 than it is with the mounting shown in FIGURE 1.

In a further variation, shown in FIGURE 4, the arrangement is identical to FIGURE 1 except that the transducer 80 is mounted directly on mandrel rod 56 and applies vibrations 'to it in the longitudinal or axial direction.

A transducer has now been developed which is capable of producing both longitudinal and lateral vibrations simultaneously or separately. In FIGURE 5 such a transducer 82 is mounted on pressure die 40 and causes it to vibrate in either or both directions, applying the vibrations to the tubing in the bending zone and some distance upstream thereof.

The damping effect of large masses is greatly reduced by the use of the arrangement shown in FIGURE 6. Here the pressure die 84 is provided with a section 86 which is movably mounted on the main body and coupled to the force generator 16 for vibrations in a direction transverse to tube 38.

A similar effect is achieved with the device of FIGURE 7 in which die 88 mounted on shaft 90, is provided with a section 92 which is movably mounted on the main body of the die and coupled to the force generator 16 for vibration in a direction transverse to the axis of the tube. Force generator 16 is supported by brackets 94 on shaft 90. This assembly, as well as those of FIGURES 8, 9 and 10, is to be used in the apparatus of FIGURE 1 in substitution for comparable parts.

Where all of the elements are very small and light to process small tubing, the entire die may be vibrated as 6 indicated in FIGURE 8, where die 96 is mounted on shaft 98 which is mounted in the machine for vertical movement, In this case, the force generator 100 is mounted on shaft 98 and transmits its vibrations thereto and therethrough to cause vertical vibration of die 96.

It is difiicult with a conventional transducer to develop sufiicient intensity to adequately soften large, thickwalled tubes. Consequently, a multiple transducer force generator has been developed for magnetostrictive transducer system and this is illustrated in FIGURE 9. In this modification, die 102 is mounted on shaft 104 which in turn is mounted in bearing support 106 for rotational vibration about its vertical longitudinal axis. The force generator comprises an annular body 108 having a central hub portion 110 which is fixedly mounted on shaft 104. A plurality of transducer units 112 are mounted in spaced relation about the periphery of the body and are oriented to produce vibratory forces in directions tangent to the periphery of the body. They are actuated in unison to produce rotational vibration of the body about the axis of shaft 104. Since their effect is additive they produce a much higher intensity than is possible with a single conventional transducer.

For very heavy duty work the basic force generator shown inFIGURE 9 may be used in combination with like force generators which, if desired, can be stacked in a number of ways. Two or more such generators may be mounted on shaft 104. They can also be stacked to produce axial vibratory motion as illustrated in FIGURE 10. In this form, the die 114 is mounted on shaft 116 which in turn is mounted in base 118 for vertical movement. A bracket 120 is fixedly mounted on base 118, and shaft 122 is rigidly connected to it. A force generator 108 is rigidly connected by its hub portion 110* to each end of shaft 122. Collar 124 fixed to shaft 116 and carries fixed outwardly extending shafts 126. The outer ends of these shafts engage in openings 128 in generators 108 at points near their peripheries. It will be seen that these points vibrate through an extremely small are which is tangent to a vertical line parallel to shaft 124. Hence, for all practical purposes, they vibrate vertically and transmit their vibrations through shafts 126 to cause shaft 116 to vibrate vertically. As many force generators as necessary may be mounted in this way.

The basic principles outlined above may be incorporated in the type of bending machine illustrated in FIG- URES 13 and 14, which is an adaptation of the well known Buffalo Rolls. This machine comprises a platform 130 movably mounted on a support or table 132 by means of columns 134 and resilient connectors 136 to permit vertical vibration. A high frequency mechanical 'force generator 138, mounted on the support, is coupled by reed or horn 140 to the platform to induce vertical vibrations therein.

A roller 142 is rotatably mounted on the platform to form the inside of the bend in tube 144. Roller 146 is mounted adjacent to roller 142 to guide the tube as it enters the bending zone. Rollers 148 and 150 are mounted on arms 152 and 154 to swing about the axis of roller 142 to various adjusted positions to define a path of travel for the tube which will produce the desired curvature. When the force generator is activated, platform 130 and all of the rollers vibrate vertically transverse to the plane of bend and create a semi-plastic condition in the material of the tube in the same way as in the previous modifications.

If it is desired to reduce the mass which must be vibrated, connectors 136 are omitted and the platform is rigidly mounted on the columns. Rollers 146, 148, and 150 are so mounted on the platform as not to vibrate, while roller 142 is vertically movably mounted to the platform and coupled directly to horn 140. With this arrangement, only the mass of roller 142 need be energized by the force generator.

In FIGURES 15 and 16 is shown a transducer 156 having a plurality of longitudinally extending faces 158, 160, 162, 164, 166 and 168. Each of said faces has a pair of matched crystals 170 and 172 mounted thereon. Each of said pair of matched crystals is energized by electrical power being supplied through lines 174 and 176. The transducer 156 has a longitudinally extending, coaxial opening 178 formed therethrough. The transducer 156 may, if desired, be coupled to an exponential horn 180. The crystal pairs operate in shear. While the forces generated may be peripherally directed, they are preferably directed parallel to the longitudinal axis of opening 178.

The transducer 156 shown in FIGURES 15 and 16 is constructed for use with a piece of tubing which is to be processed through the opening 178 while the transducer 156 is energized by the sets of matched crystals 170 and 172. It will be appreciated that when the transducer 156 as shown in FIGURES 13 and 14 is used in combination with a suitable system, such as the rollers 146, 148 and 150 shown in FIGURES 15 and 16 which are positioned downstream of transducer 156, i.e., in the line of tube travel, that a unique method and apparatus will be achieved for bending tubes. More specifically, the input frequency to each pair of matched crystals 170 and 172 results in energy being transmitted to the tube while the tube is passing through the opening 178. In addition, one or more of the rollers 146, 148 and 150 as shown in FIGURES 13 or 14, or other different combinations as may be desired or required, are likewise subjected to a similar type of input frequency. The combination of transducer 156 with the agitator rollers as aforementioned facilitates the formation of tube bending in a large number of varied forms but with a minimum of equipment. Understandably, the tube or pipe is pushed through the orifice opening 178.

In FIGURE 17 is shown a modification of a conventional tube bending machine which uses a rotatably mounted, piezo-electric crystal actuated roller 182 in lieu of the conventional straight pressure die. Roller 182 is mounted for rotation upon axle 184. Roller 182 is shown with four sets of piezo-electric crystals 184 mounted thereon. Each of the piezo-electric crystal sets 184 are similar to the matched piezo-electric crystals 170 and 172 as shown in FIGURES 15 and 16. Each of the piezo-electric crystals 184 are actuated by electrical power being supplied thereto through lead lines 186 and 188. During the bending operation, roller 182 will travel in the direction indicated by arrow 190. Also, with the crystals 184 mounted as shown, roller 182 will function similarly as a pressure die boost, i.e., it will reduce the adverse effects caused by elongation of the metal in the adjacent portions of the tube while at the same time exerting a compressive force against the surface of the tube. In FIGURE 17 is also shown a bend die 192 and a clamping die 194. A tube 196 is shown mounted between roller 182 and bend die 192. It will be appreciated that a tube bending apparatus constructed in this manner will benefit from the substantial reduction in overall mass associated with conventionally available apparatuses.

In FIGURE 18 is shown an enlarged, cross-sectional view of the wall of a tube 198 which has been bent. In FIGURE 18, the area encompassed by broken line 200 is the deformation zone involved for tubes bent in the conventional manner. The area included within broken line 202 shows the deformation zone for a tube bent in accordance with the method and apparatus of the herein invention. It will be readily obvious that the area encompassed by broken line 202 is substantially greater than the area encompassed by broken line 200. The beneficial results obtained from this will now be readily obvious in view of the illustration shown in FIGURE 18 and the description contained above with respect to FIGURES l1 and 12. In FIGURE 18, lines 206 and 207 show the inner and outer surfaces of the wall segment 208 of tube 198. These surfaces are formed when the tube 198 is bent in the conventional manner. Lines 210 show the corresponding surfaces of wall segment 208 when the tube 198 is bent in accordance with the method and apparatus of the herein invention. Similarly, the inner surface 212 of Wall segment 214 is illustrative of the condition existing when a tube has been bent with conventional tube bending equipment. The line 216 shows the same surface when the tube 198 has been formed in accordance with the method and apparatus of the herein invention. It has been found that the area 202 extends outwardly beyond the area 200 by an amount equal to approximately the diameter of the tube. This increased stretch area is responsible for the reduction in thinning obtained for the outer wall segment of the bent tube and the reduction in thickening obtained for the inner wall segment of the bent tube.

In view of the foregoing, it will now be readily ap parent that a unique method and apparatus for bending tubes has been described. The apparatus and method of the subject invention are characterized in a number of ways. For example, with prior art bending techniques and equipment it was extremely difiicult, if not impossible, to obtain a bend having a radius of a curvature of less than the diameter of the tube so bent. Additionally, for tubes formed from exotic materials such as titanium, Inconel and Hastelloy, it was found that a bend having a radius of curvature less than three times the diameter of the tube being bent could not be formed. However, with the method and apparatus of the herein invention, it is now possible to exceed these limitations quite readily.

As previously indicated, the method and apparatus of the subject invention enables the bending of tubes formed from materials having adverse elongation properties. Further, the rate of tube bending has been greatly increased because of the substantial reduction in time required for the metal to flow during bending, i.e., with the unpinning of the particles in the crystal lattice it has been found that the metal will flow as rapidly as the tube can be deformed. Further, with the unpinning of the particles in the crystal lattice, it has been found that the grains fall into alignment with less residual stress.

Another advantage of the instant invention is the ability to bend tubes even though same have been poorly annealed. As a matter of fact, in some applications, tu-bes may be bent even though same have become work hardened.

A further advantage of the instant invention is the reduction of incidence of wall collapse which occurs from excessive thinning particularly where a thin walled tube is involved.

Another advantage of the instant invention is that tube bending may be accomplished without the use of lubricants thereby negating cleaning of the tube and tooling following the bending operation.

Another advantage of the instant invention is that there is less spring back following bending thereby permitting a more accurate bend to be made.

An additional advantage of the subject invention is that a finer grain crystal structure is obtained which provides a tougher timbre than has heretofore been possible for tubes bent in accordance with the conventional techniques and equipment.

Still another advantage of the subject invention is that tubes may be bent with a small radius of curvature without undue incidence of wrinkling on the compressive portion of the bend.

Still another advantage of the subject invention is substantially increased degree of finish on the bent tube including a substantial elimination of orange peel effect and possible subsequent structural failure as the result thereof.

Another advantage of the instant invention is that good quality bends may be obtained even though poor tooling tolerances are involved and poor set up practices are utilized.

Another advantage obtained is the availability of tube bending equipment substantially reduced in overall mass.

It will be apparent to those skilled in the art that various changes may be made in the operation of the method and the construction of the apparatus without departing from the spirit of the invention, and it is intended that all such changes shall be embraced Within the scope of the following claims.

I claim:

-1. Apparatus for bending tubing to a desired curved shape, comprising: a support; a plurality of relatively movable tooling means on said support and defining a bending zone; said tooling means being adapted to guide a tubing workpiece through said bending zone and to apply forming forces to said workpiece to bend at least a portion thereof into a curved shape; and a high frequency mechanical force generator coupled to at least a portion of said tooling means to impart vibratory forces thereto; said portion of said tooling means being adapted to be in direct mechanical contact with the workpiece to transmit the vibratory forces to the workpiece and substantially reduce its resistance to bending forces applied to it at the bending zone.

2. Apparatus as claimed in claim 1; the force generator being so coupled to the tooling means that the latter is adapted to apply the vibratory forces to the workpiece in a direction generally parallel to its axis.

3. Apparatus as claimed in claim 1; the force generator being so coupled to the tooling means that the latter is adapted to apply the vibratory forces to the workpiece in a direction substantially lateral with respect to its axis.

4. Apparatus as claimed in claim 1; said tooling means including a platform movably mounted on said support and a plurality of grooved rollers rotatably mounted on said platform; said rollers being adjustable to define a path of travel between them for a workpiece to achieve a desired curvature; and said force generator being coupled to said platform to cause the platform and said rollers to vibrate in a direction transverse to the plane of bend.

5. Apparatus as claimed in claim 1; said tooling means including a platform mounted on said support and a plurality of grooved rollers rotatably mounted on said platform; said rollers being adjustable to define a path of travel between them for a workpiece to achieve a desired curvature; and said force generator being coupled to one of said rollers to cause it to vibrate in a direction trans verse to the plane of bend.

6. Apparatus for bending tubing to a desired curved shape, comprising: a support; a plurality of relatively movable tooling means on said support and defining a bending zone; said tooling means includin a pressure die to guide a tubing workpiece through said bending zone and provide a support against lateral displacement loads and a rotatable bend die to apply forming forces to said workpiece to bend at least a portion thereof into a curved shape; and a high frequency mechanical force generator coupled to at least a portion of said tooling means to impart vibratory forces thereto; said portion of said tooling means being adapted to be in direct mechanical contact with the workpiece at said forming zone to transmit the vibratory forces to the workpiece and substantially reduce its resistance to forces applied by said bend die.

7. Apparatus as claimed in claim 6; the input frequency of vibration of said force generator being in the range of 18,000 to 100,000 cycles per second.

8. Apparatus as claimed in claim 6; said tooling means including a mandrel having a support end at said forming zone adapted to be located within a workpiece in contact with its inner wall to support the workpiece against collapse a'nd to transmit vibratory forces thereto; a mandrel extension rod extending away from said forming zone; and said force generator being coupled to said rod to transmit vibratory forces therethrough to said support end.

9. Apparatus as claimed in claim 8; said force generator being so coupled to said rod as to apply the vibratory forces thereto transversely of the axis of the rod.

10. Apparatus as claimed in claim 8; said force generator being so couppled to said rod as to apply the vibratory forces thereto along the axis of the rod.

11. Apparatus as claimed in claim 6; said force generator being so coupledto said bend die as to apply the vibratory forces thereto in a direction along the axis of rotation of said bend die.

12. Apparatus as claimed in claim 6; said force 'generator being so coupled to said bend die as to apply the vibratory forces thereto in a sense of rotation about the axis of rotation of said bend die.

13. Apparatus as claimed in claim 6; said bend die including an independent section oscillatably mounted to the main body of said bend die; and said force generator being coupled to said independent section to cause it to vibrate with respect to said main body and apply the vibratory forces to the workpiece during rotation of the bend die.

14. Apparatus as claimed in claim 6; said pressure die being movably mounted with respect to said support; and said force generator being coupled to said pressure die to cause it to vibrate and apply the vibratory forces to the workpiece during rotation of the bend die.

15. Apparatus as claimed in claim 14; said force generator being adapted to cause vibration of said pressure die in a direction parallel to the longitudinal axis of the workpiece and in a direction transverse to the longitudinal axis of the workpiece simultaneously.

16. Apparatus as claimed in claim 6; said pressure die including an independent section oscillatably mounted to the main body of said pressure die; and said force generator being coupled to said independent section to cause it to vibrate with respect to said main body and apply the vibratory forces to the workpiece during rotation of the bend die.

17. A high frequency mechanical force generator comprising: an annular body having a central hub portion for mounting on a support shaft; and a plurality of high frequency force generator units mounted in spaced relation about the periphery of said body; said units being oriented to produce vibratory forces in directions tangent to the periphery and acting in unison to produce high intensity rotational vibration of said body about an axis passing through said hub portion perpendicular to the plane of said body.

'18. Apparatus as claimed in claim 17 and, in addition thereto; a support; a shaft having a longitudinal axis and mounted on said support for rotation about said axis; a bend die mounted on said shaft; and said force generator being fixedly mounted on said shaft to impart its rotational vibrations to said shaft and said bend die.

19. Apparatus as claimed in claim 17 and, in addition thereto; a support; a first shaft having a longitudinal axis and mounted on said support for oscillatory movement along said axis and rotation about said axis; a bend die mounted on said first shaft, a second shaft fixedly mounted on said support spaced from said first shaft and extending in a direction perpendicular to the axis of said first shaft; said force generator being fixedly mounted by its hub portion to said second shaft and lying in a plane parallel to the axis of said first shaft; and coupling means extending between said first shaft and a point near the periphery of said force generator where said periphery is tangent to a line parallel to the axis of said first shaft; the tangential vibratory motion of said force generator serving to produce axial vibratory motion of said first shaft.

20. A method of bending tubing with reduced power application in an apparatus having a bending zone, a 'bend die at the bending zone, and a mandrel having a free end at the bending zone, comprising: securing a length of tubing to the bend die; inserting the mandrel in the tubing with its free end at the bending zone; and rotating the bend die to draw successive portions of the length of tubing through the bending zone to form a bend of desired extent and curvature; and applying high frequency vibratory mechanical energy to the portions of the tubing and mandrel at the bending zone during the bending operation to generate and propagate surface waves having the property of greatly reducing the frictional drag between the mandrel and the tubing.

21. A method of bending tubing in an apparatus having a bending zone and a bend die at the bending zone, comprising: securing a length of tubing to the bend die; and rotating the bend die to draw successive portions of the length of tubing through the bending zone to form a bend of desired extent and curvature; and applying high frequency vibratory mechanical energy to the por tions of the tubing successively passing through the bending zone during the bending operation; said energy being sufiiciently intense to render the tubing material at the bending zone semi-plastic and reduce its resistance to shear stress and plastic deformation.

22. A method of bending tubing in an apparatus having a. bending zone, a bend die in the bending zone, and a mandrel having a free end at the bending zone, comprising: securing a length of tubing to the bend die; inserting the mandrel in the tubing with its free end at the bending zone; and rotating the bend die to draw successive portions of the length of tubing through the bending zone to form a bend of desired extent and curvature; and applying high frequency vibratory mechanical energy to References Cited UNITED STATES PATENTS 2,792,048 5/1957 Fuchs 72-150 2,841,201 7/1958 Cheatle 72-141 2,962,077 11/1960 Condiif 72-149 X 2,996,100 8/1961 Newhall et al. 72-369 3,147,792 9/1964 Hautau 72-150 3,209,572 10/1965 Boyd et al. 72-277 3,240,048 3/1966 Callendar 72-369 MILTON S. MEHR, Primary Examiner US. Cl. X.R. 

